湿骨内动态力—电电位的因素分析

本文通过实验测出了在动态压力作用下缓冲液自板形骨试件的不同表面流入时的动态力－电电位波形。修正了以前的结论，分析了瞬态和稳态时力－电电位产生的原因，证明无论瞬态还是稳态时的力－电电位主要产生于流动电位而并非压电效应。     

骨的力–电效应研究方法与进展

骨组织在受到应力作用(正常的生理活动)变形后在骨内产生电位的现象称为骨的力–电效应,它主要包括压电效应和动电效应.研究骨在动态过程中产生的电位幅值和分布特点,不仅是了解电刺激骨生长机理的必要步骤,也是实现骨治疗和重建的生理基础.它一方面是用数学方法来描述外力作用下其电位大小与应力、应变、应变率及加载速率的关系,另一方面是考察生理环境(pH值、离子浓度、温度、湿度等)对电位的影响.首先对力–电理论进行了简单的介绍,重点总结了其研究方法,包括理论模型和分离式霍普金生杆冲击、弯曲变形及缓冲液中的动态测试等实验方法.此外,对骨替代材料和牙本质领域的力–电效应研究也进行了一定的综述.     

骨的力电性质

骨的力电性质包括两个来源,压电效应和动电现象。骨力电性质的研究是包含力学、物理学、化学、生物学和生理学等多学科的综合性课题。本文分别介绍了骨压电效应和动电现象的基本机理、产生原因、研究方法和研究结果。      

非线性压电效应下压电弯曲执行器的弯曲

研究压电弯曲执行器在强电场作用下的非线性弯曲行为。考虑电致伸缩和电致弹性的非线性压电效应,导出了压电悬臂执行器自由端挠度或激励力和作用电场之间的非线性关系。结果表明,考虑非线性压电效应在很大的电场范围内都与实验结果吻合得很好,而线性压电效应只适合于低电场的情况。     

加载速率对骨的流动电位的影响

骨受力变形时所引起的压力驱动骨内哈佛氏管或骨小管内的液体流动,是骨内出现流动电位的外部原因.由于人体经常受动态载荷作用,研究骨在动态加载过程中流动电位的变化,更有助于了解骨细胞周围电环境的性质.为此,设计了流动电位测试系统,在骨试样两端施加梯形压力波.实验测量了在不同加载速率下流动电位的变化波形.结果显示,加载速率越高,流动电位有减小的趋势.分析认为这是由于微管中局部产生的湍流引起的.     

湿度对骨内压电信号的影响

对不同相对湿度下的骨压电电压和压电电荷信号进行测量研究,来考察湿度对骨压电信号的影响.采用三点弯曲干骨试样,以梯形脉冲载荷的方式进行加载,分别应用超高输入阻抗的生物信号放大器和电荷放大器测量了三种不同相对湿度下的骨压电电压和压电电荷信号波形.结果表明,骨压电电压峰值随湿度的增加而下降很快,当湿度从30%增至60%时,电压降幅达到了80%左右;基于测试原理的不同,骨压电电荷也随湿度的增加而下降,其降幅较小.由此可以推断,骨在体内湿润的状态下,受力变形时压电电压幅值可能趋于零.电荷的产生和瞬时泄放有可能是骨在体内的动态载荷作用下的压电效应的表现形式.     

切应力对牛骨蠕变变形的影响研究

骨尤其是湿骨,在恒定载荷作用下会发生蠕变变形。为了确定切应力是否影响骨的蠕变变形,采用对骨薄板试样分别施加集中载荷和均布载荷的方式,测量试样挠度实时的变化曲线。结果显示,在载荷恒定时,骨试样的挠度随时间不断增加,体现了典型的蠕变特性。集中荷载下骨的蠕变变形远大于均布荷载下骨的蠕变变形,湿骨的蠕变位移比干骨高近7倍。分析认为,对试样粘弹性性质的影响不仅有正应力的作用,也有切应力的作用;切应力产生的蠕变变形约为正应力所产生蠕变变形的0.85倍。     

交变电场作用下骨表面温升的实验研究

骨具有力电性质,这一性质可促进骨组织生长。骨既是生理器官又是介电材料,在交变电场作用下,其表现行为可能有生理作用。为此,本文测量了骨悬臂梁试样在交变电场下的表面温升与顶端挠度。发现在电压70V,频率为10~70kHz的交流电场下,最大表面温升达到2~4℃,最大挠度变化为9.0~78.7μm;在频率10kHz,电压为70~175V的交流电场下,最大表面温升达到4~6℃,最大挠度变化为13.0~114.3μm。同时测量了两种经典介电材料有机玻璃和聚乙烯在交变电场下的温升与顶端挠度,最大温升低于0.5℃,但是挠度与骨试样相当,所以相对高温升是骨特有的性质。将交流电压有效值替换成相同幅值的直流电压时,最大温升也低于0.5℃,基本没有挠度变化,所以相对的高温升反映了骨的交流性质。分析后认为,骨在交变电场作用下的温升由胶原的介电损耗引起。实验数据显示,骨在交变电场下,表面温度变化与加载电压的平方成正比,且在实验加载的10~70kHz频段内,骨的介电常数随频率的变化明显。     

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利用模拟装置实现了卡瓦与套管在地面上的实验，使用电测的方法测量胀卡时套管外表面的应变．由实验数据获得计算网格节点处的应变，同时利用单位咬合力作用套管的有限元结果进行数值法计算，获得卡瓦各咬合齿对套管咬合力的分布，为卡瓦的优化设计提供了可靠数据．     

强电场和机械荷载联合作用下压电层合梁的非线性变形

本文研究简支,固支和悬臂压电层合梁在强电场和机械荷载联合作用下的非线性变形。考虑材料的电致伸缩和电致弹性压电效应以及几何非线性导出压电层合梁的数学模型。并求得在电场和均布力联合作用下各种边界条件梁的挠度和位移解析表达式。通过对双压电晶片梁和单压电晶片梁的数值计算及分析得到线性与非线性模型之间的差别和适用范围。     

Finite Element Studies on the Role of Mechanical Loading in Bone Response Around Oral Implants*

Inappropriate implant loading has been suggested as one of the most important factors for late failures of endosseous oral implants. In order to quantify peri-implant bone stresses and strains for a controlled load applied during an animal experiment, an anatomical finite element model was built. Marginal bone loss that occurred during the animal experiment could only partially be related to overload. Furthermore, it is hypothesised that relative motion between bone and implant could have also played a role in the marginal bone response. In order to further explore the relation between marginal bone resorption and overload, a computer algorithm was developed that simulates overload-induced marginal bone loss. It was found that marginal bone resorption can be arrested due to a redistribution of the peri-implant bone stresses.     

青鱼鳍骨、肋骨和鳃盖骨微观结构与力学性能的比较研究

本文从材料学角度定量分析了青鱼鳍骨、肋骨、鳃盖骨的微观结构、成分及力学特性。利用电子显微镜观察了鳍骨、肋骨、鳃盖骨的微观结构;通过X射线衍射、电镜能谱以及煅烧的骨灰综合分析,探讨了青鱼鳍骨、肋骨、鳃盖骨的有机、无机成分之间的密切联系;进行了青鱼鳍骨、肋骨、鳃盖骨的拉伸实验;利用显微硬度计对干、湿状态下的鳍骨、肋骨、鳃盖骨进行了硬度测试。结果显示,鳍骨无机物含量较多,鳃盖骨有机物较多,肋骨介于两者之间;矿化胶原蛋白束在鳍骨中的排列非常规则,在鳃盖骨中排列不是很规则,在肋骨中排列较规则;鳍骨中矿化胶原纤维束间孔洞非常少,骨质密实,而在腮盖骨中孔洞很多,骨质稀疏;干的鱼骨显微硬度均大于湿的鱼骨。结论是,鳍骨、肋骨、鳃盖骨的微观结构、成分及力学特性存在差异,其中鳍骨的力学性能明显强于鳃盖骨,肋骨介于二者之间,水份对青鱼鳍骨、肋骨、鳃盖骨的硬度有明显的影响。     

Fluid Flow Analysis of Integrated Porous Bone Scaffold and Cancellous Bone at Different Skeletal Sites: In Silico Study

The dynamic characteristic of bone is its ability to remodel itself through mechanobiological responses. Bone regeneration is triggered by mechanical cues from physiological activities that generate structural strain and cause bone marrow movement. This phenomenon is crucial for bone scaffold when implanted in the cancellous bone as host tissue. Often, the fluid movement of bone scaffold and cancellous bone is studied separately, which does not represent the actual environment once implanted. In the present study, the fluid flow analysis properties of bone scaffold integrated into the cancellous bone at different skeletal sites are investigated. Three types of porous bone scaffolds categorized based on pore size configurations: 1 mm, 0.8 mm and hybrid (0.8 mm interlaced with 0.5 mm) were used. Three different skeletal sites of femoral bone were selected: neck, lateral condyle and medial condyle. Computational fluid dynamics was utilized to analyze the fluid flow properties of bone scaffold integrated cancellous bone. The results of this study reveal that the localization and maximum value of shear stress in an independent bone scaffold are significantly different compared to the bone scaffold integrated with cancellous bone by about 160% to 448% percentage difference. Low shear stress and high permeability were found across models that have higher Tb.Sp (trabecular separation). Specimen C and femoral lateral condyle showed the highest permeability in their respective category.

     

Experimental Evaluation of Strain Shielding in Distal Femur in Revision TKA

Theoretical concerns about the use of cemented and press-fit stems in revision total knee arthroplasty (TKA) include stress shielding with adverse effects on prosthesis fixation. Radiological studies have showed distal femoral bone resorption after revision TKA. The revision with use of stems can place abnormal stresses. These stresses can promote the effect of bone stress shielding and may contribute to bone loss. Experimental quantification of strain shielding in the distal synthetic femur following TKA is the main purpose of the present study. Three different constructs of TKA were assessed. The first construct included a stemless femoral component. The other two included a press-fit and a cemented femoral stem. Cortical bone strains were measured experimentally with tri-axial strain gauges in synthetic femurs before and after in-vitro knee surgery. The difference between principal strains of implanted and intact femur was calculated for each strain gauge position. This study indicates that the use of stems in distal femur changes the distribution and magnitude of bone strains. The press-fit stem provoked relevant bone area (stem length) subjected to strain shielding and also originated the highest reduction of strains in the distal region, which can potentially induce bone resorption. The stemless implanted femur produced minor bone strain changes relatively to the intact femur. The use of distal femur stems increases initial stability in the bone, but the observed reduction of strains in this region, relative to the intact femur, provokes strain shielding that can induce bone resorption and may compromise the long term implant stability.     

Optimal internal architectures of femoral bone based on relaxation by homogenization and isotropic material design

The influence of the loading conditions on the trabecular architecture of a femur is investigated by using topology optimization methods. The response of the bone to physiological loads results in changes of the internal architecture of bone, reflected by a modification of internal effective density and mechanical properties. The homogenization based optimization model is developed for predicting optimal bone density distribution, wherein bone tissue is assumed to be a composite material consisting of a mixture of material and void. The homogenization scheme treats the geometric parameters of the microstructures and their orientation as design variables and homogenizes the properties in that microstructure, which is generally anisotropic. The penalization of the optimal material density then leads to a classical optimal structure which consists of regions with bone material and regions without bone material. The IMD (Isotropic Material Design) approach is next applied to determine the optimal elasticity tensor in terms of the bulk and shear moduli for the present loading applied to the femoral bone sample. IMD is able to provide both the external shape and topology together with the optimal layout of the isotropic moduli. Both topology optimization methods appear to be complementary. Simulations of the internal bone architecture of the human proximal femur results in a density distribution pattern with good consistency with that of the real bone.     

Osteoporosis affects both post-yield microdamage accumulation and plasticity degradation in vertebra of ovariectomized rats

Estrogen withdrawal in postmenopausal women increases bone loss and bone fragility in the vertebra. Bone loss with osteoporosis not only reduces bone mineral den-sity (BMD), but actually alters bone quality, which can be comprehensively represented by bone post-yield behav-iors. This study aimed to provide some information as to how osteoporosis induced by estrogen depletion could influence the evolution of post-yield microdamage accu-mulation and plastic deformation in vertebral bodies. This study also tried to reveal the part of the mechanisms of how estrogen deficiency-induced osteoporosis would increase the bone fracture risk. A rat bilateral ovariectomy (OVX) model was used to induce osteoporosis. Progressive cyclic compression loading was developed for vertebra testing to elucidate the post-yield behaviors. BMD, bone volume fraction, stiffness degradation, and plastic deformation evo-lution were compared among rats raised for 5 weeks (ovx5w and sham5w groups) and 35 weeks (ovx35w and sham35w groups) after sham surgery and OVX. The results showedthat a higher bone loss in vertebral bodies corresponded to lower stiffness and higher plastic deformation. Thus, osteo-porosis could increase the vertebral fracture risk probably through microdamage accumulation and plastic deforming degradation.     

考虑载荷特性的骨重建力学调控机制

骨组织具有适应变化力学环境的能力.通过分析骨组织适应力学环境的调控机制,吸纳工程强度设计准则思想,提出考虑载荷特性的骨重建力学调控机制,探讨载荷特性对力学激励的影响,对牙槽骨“张力区骨增生和压力区骨吸收”的现象进行分析和数值模拟.结果表明考虑载荷特性的骨重建力学调控机制是合理的,是骨重建力学调控机制理论的补充和完善.     

A mathematical model of cortical bone remodeling at cellular level under mechanical stimulus

A bone cell population dynamics model for cortical bone remodeling under mechanical stimulus is developed in this paper. The external experiments extracted from the literature which have not been used in the creation of the model are used to test the validity of the model. Not only can the model compare reasonably well with these experimental results such as the increase percentage of final values of bone mineral content (BMC) and bone fracture energy (BFE) among different loading schemes (which proves the validity of the model), but also predict the realtime development pattern of BMC and BFE, as well as the dynamics of osteoblasts (OBA), osteoclasts (OCA), nitric oxide (NO) and prostaglandin E₂ (PGE₂) for each loading scheme, which can hardly be monitored through experiment. In conclusion, the model is the first of its kind that is able to provide an insight into the quantitative mechanism of bone remodeling at cellular level by which bone cells are activated by mechanical stimulus in order to start resorption/formation of bone mass. More importantly, this model has laid a solid foundation based on which future work such as systemic control theory analysis of bone remodeling under mechanical stimulus can be investigated. The to-be identified control mechanism will help to develop effective drugs and combined nonpharmacological therapies to combat bone loss pathologies. Also this deeper understanding of how mechanical forces quantitatively interact with skeletal tissue is essential for the generation of bone tissue for tissue replacement purposes in tissue engineering.